In digital data transmission networks, such as in cellular radio networks, different analyzers and simulators for measuring the operation of the network are used. Analyzers can be used for monitoring data transmission connections between a cellular radio network and a subscriber terminal, for example.
Publication U.S. Pat. No. 5,884,175 discloses a method and an apparatus for monitoring data transmission transactions in a mobile network. The method of the publication comprises monitoring a first signaling channel, and detecting a first signaling transaction, which is transferred out of the monitored cell with handover, and at least one predetermined message parameter is captured from the transaction. In addition, the method comprises monitoring a second signaling channel and detecting a signaling transaction (handover) with which the transfer to the cell takes place, and capturing said at least one predetermined message parameter from the transaction. Further, the method comprises comparing values of parameters captured in the preceding phases, and if the values are the same, it is concluded that the first and the second transaction belong together.
The described method does not function in all mobile networks, because there are not always common parameter values, in which case monitoring handovers with the method fails, and thus monitoring calls by using the method fails too.
It is difficult to monitor the lub interface of a 3G cellular radio network because monitoring protocols used on AAL2 (ATM Adaptation Layer Type 2) connections requires capturing the configuration information of the protocols from the configuration messages transmitted to a mobile phone and from the configuration messages transmitted to a base transceiver station. In a case of handover, the subscriber terminal moves from one base transceiver station to another, whereby configuration messages of a radio link are transmitted to the new base transceiver station, but no configuration messages of the connection are transmitted to the subscriber terminal via the new base transceiver station any more. If the interface monitoring is distributed between two devices and the handover takes place between the devices, the receiving apparatus has no information on configuration messages of the subscriber terminal, so that decoding of protocols cannot be performed.
The problem can be solved in such a way that the device monitoring the new channel attempts to identify the correct configuration of the protocols. However, this takes processor time and can lead to incorrect decoding results. In addition, it is not necessarily possible to specify the signaling of which subscriber terminal is monitored, and so the call tracing fails. Automatic identification of protocols may also be needed because it is not always possible to monitor the signaling transaction from the beginning. Thus, the connections that are not monitored from the beginning cannot be configured with configuration based merely on monitoring messages.
Another possibility is that the monitoring is performed with one device. This is problematic, however, because different interfaces can be positioned far away from each other (e.g. in a case of Abis/lub interfaces), whereby the problem is the transfer of messages from the interfaces to the device to be monitored; the problem is also that the performance of one device is not necessarily sufficient for monitoring all cells.
When tracing calls, it is necessary to be able to monitor the call when handover is taking place. The user identifier is usually visible in the network to be monitored only at the beginning of the call. So in a case where the start of a call is monitored with a first analyzer and where the call is transferred with handover to an interface monitored by a second analyzer, the call cannot be identified on the second interface, and thus call tracing cannot be performed. In call tracing, the problem is both the configuration of the connections to be monitored and the monitoring of handovers.